Ink jet printing systems are susceptible to turbulent air streams and paper dust, contamination that affect the proper functioning of the print head. Several methods of protecting the regions surrounding the print head from contamination have been established, such as by enclosing the print head and filling the enclosure with filtered air under positive pressure.
FIG. 1 is an example of such a prior art system, wherein a print head assembly is provided with a print head interface controller enclosure 1 having an air inlet fan 2 adapted to force air into enclosure 1 through a replaceable air inlet filter 3. The filter reduces the amount of foreign debris from the internal components of the print head. The air stream through the print head assembly continues from air inlet fan 2, around a manifold 4, into a manifold filter 5, and into a print head 6. The direction of print media travel past the print head is illustrated in FIG. 1 by a dotted line arrow 7, while air stream direction is depicted by a set of arrows 8.
While these structures have greatly reduced particle-based malfunctions, the prior art has not addressed the issue of non-straight ink droplet trajectories caused by turbulent air streams between print head nozzle openings and the print media (herein referred to as the “printing region”). The straightness of the ink droplet trajectories is vital to the proper placement of droplets onto a print medium. When turbulent air streams occur within the printing region, the affected jet causes misregistration of droplets and less than desired print quality.
Air turbulence in the printing region has at least two sources. Air turbulence is generated by air inlet fan 2 itself as it generates the air stream. Turbulence is also generated when high velocity air turns around objects and interfaces. These objects and interfaces may be corners and edges of the print head structure or may even be dirt particles and debris that has settled on interior surfaces of enclosure 1. The objects and interfaces can trip the air boundary layer and decrease laminar airflow, thus increasing the variation in the speed and/or direction of the air stream. These air stream variations can be sufficient to change the speed and direction of ink droplets ejected from the print head.
The air streams are necessary for cooling and contamination reduction, but the turbulence within the air stream needs to be controlled to inhibit print artifacts. Accordingly, it is an object of the present invention to reduce the turbulence of an air stream in a print head.